(CNN)Eden Carlson's story might be one in a million.
The toddler, who suffered brain damage after falling into a swimming pool at 23 months old, has begun to rebuild her brain function after treatment with hyperbaric oxygen therapy, according to a case study published last month in the journal Medical Gas Research.
"We're stimulating growth of tissue and inhibiting inflammation and stopping cell death," said Dr. Paul G. Harch, clinical professor and director of hyperbaric medicine at LSU Health New Orleans School of Medicine.
Hyperbaric oxygen therapy introduces a greater-than-usual amount of oxygen to patients within a special chamber. The special chamber allows a doctor to control both the pressure and the level of vital gas, explained Harch, who treated the child and is lead author of the case study.
After months of oxygen treatments, Eden is a "typical 3-year old," said her mother, Kristal Carlson of Fayetteville, Arkansas.
"Her cognitive abilities and speech are completely recovered. Most of her fine motor skills have returned," Carlson wrote in an email. "Today she walks with assistance really well. She can walk independently, also, but not long distances."
A mother's nightmare
While Carlson was in the shower on February 29, 2016, Eden, who had just learned to walk, slipped through a baby gate and fell into the backyard swimming pool.
"Her older siblings lost track of her and thought she was with me," explained Carlson, who is still unsure how long Eden may have been in the water.
It could have been "as long as 15 minutes," she said, but was "at least five minutes."
Also unclear is how long her heart stopped beating, Harch said.
"She stopped breathing, obviously, once she was face-down and probably inhaled some water, but we don't know how long after that her heart stopped and her blood pressure went to zero," Harch said. "We just know that when Mom got her out of the pool, there was nothing."
Carlson said her first instinct was to get her daughter to breathe.
"So I gave her a couple of breaths and patted her, saying her name," Eden's mother said. "Then chest compressions." Paramedics took over CPR, which was delivered for 100 minutes before Eden's heart began beating on its own.
Stabilized, the child was flown to Arkansas Children's Hospital, where she spent five weeks, her mother recalled. "When we brought her home, she was a vegetable, unable to do anything," she said. "She had a feeding tube, could not speak, could not sit up, etc."
"She was profoundly injured," Harch said. The hospital sent the child home with a monitor because when she'd fall asleep, she'd stop breathing at times and needed her parents to resuscitate her. "The predictions given to the family by the doctors were a list of never-evers: She will never ever talk, walk or eat on her own."
It soon became clear that the doctors and neurologists at Arkansas Children's Hospital could do nothing more for Eden, so her parents "started googling alternative ways to treat brain injuries," Carson explained. They found Harch's website about three weeks after returning home from the hospital and "went from there."
Eden could not be moved, and no hyperbaric oxygen chambers could be found in the Fayetteville area, so Harch treated the girl remotely with a "bridging therapy."
Using a normal oxygen tank with tubes to the nose, Harch put the child on "just 2 liters per minute for 45 minutes a day," with the first treatment exactly 55 days after Eden fell into the pool.
"We noticed an immediate difference in her," her mother said. She videotaped Eden's response to send to Harch.
He said he saw a positive change in the child's affect and decided to continue the treatments for three weeks.
"She was more relaxed, her neuro-storming stopped, she started smiling, laughing, swallowing, tracking with her eyes, and saying words," Carlson said.
When Eden's condition stabilized, her parents took her to New Orleans for treatments in a hyperbaric chamber, using the same amount of oxygen but with added pressure.
The treatments are spaced out over time in order to allow the brain to improve on its own, said Harch, who is also a co-owner of Harch Hyperbarics Inc., a consulting company.
"She began saying more words and speaking in sentences," her mother said. "She started sitting up, crawling, pulling to stand, and trying to walk!"
The ultimate proof: An MRI scan taken 162 days post-drowning -- 27 days after Eden's 40th oxygen session -- compared with one taken in the hospital shows only mild residual injury to the brain, plus a near-complete reversal of brain shrinkage that sometimes occurs in similar cases.
How does hyperbaric medicine work?
"It's not completely understood," Harch said, explaining that in the late 1950s, doctors in the Netherlands began experimenting with trying to give maximum amounts of oxygen to patients with conditions in which lack of oxygen was a problem, such as gangrene.
The US Navy also uses hyperbaric oxygen therapy to treat decompression sickness or diver's disease.
It wasn't until 2008 that the medical profession really began to understand "what this therapy is about," Harch said. "Some doctors took human cells, put them in a Petri dish and put them in a hyperbaric chamber and gave them a typical treatment." They used mass gene array analysis to measure and analyze gene activity.
"What they found at the end of 24 hours, 8,101 human genes had either been turned on or turned off, and the largest clusters were those that code for growth and repair hormones -- in other words, stimulate tissue growth and heal wounds -- and the anti-inflammatory genes," Harch said. "And the largest clusters of the turned-off ones -- and these are temporary, the turning on and turning off of genes -- were the pro-inflammatory genes and the ones that code for cell death."
Dr. Justin Sempsrott, executive director of Lifeguards Without Borders and medical director of International Surf Lifesaving Association, said Eden's case is "remarkable" and "shows future direction for rehabilitation after non-fatal drowning."
Sempsrott, who was not involved in Eden's treatment or the case study, noted that it was "done in an academically rigorous way."
"The most important determining factor of whether or not a person -- adults or children -- is going to survive drowning is how long they were under water," Sempsrott explained. For those known to be underwater for fewer than five minutes, 86% survive with good neurological outcome, and when it's less than 10 minutes, 77% survive with good neurological outcome.
People underwater for 15 to 25 minutes are "kind of all over the place," Sempsrott said. "More than 25 minutes is universally bad outcomes; they are typically neurologically devastated."
This is one reason giving breath along with good-quality chest compression is recommended for drowning resuscitation, he said.
Cold vs. warm water
"It's possible to maintain that oxygenation even for a long period of time when someone comes out of the water," Sempsrott said. "The time she was given CPR and survived is really not unheard of."
Generally, though, CPR cannot distribute oxygen throughout the body as effectively as natural breathing.
Though Harch believes that the cold water in the pool was protective, Sempsrott said that "overwhelmingly," most people who fall into cold water are simultaneously dying of hypothermia and drowning. "Hibernation state" does not help preserve the organs from harm, he said, though this is a common misperception.
"They actually have either worse or the same outcomes," he said.
In most cases, Semsprott said, "after the news story dies down," the person with little to no brain function requires round-the-clock care for the rest of their lives.
"Non-fatal drowning is far more common than fatal drowning," he said. A conservative estimate is that for every drowning, there are four non-fatal events, while the Centers for Disease Control and Prevention tallies seven non-fatal events for every drowning among children.
Dr. Paul S. Auerbach, Redlich Family Professor in the Department of Emergency Medicine at the Stanford University School of Medicine, said "prevention is the name of the game."
"Parents need to understand all the best methods for trying to prevent drowning in children," said Auerbach, whose complete list of tips in his classic book, "Wilderness Medicine," begins with the single most important rule:
Watch your children.
"Toddlers are at greatest risk for drowning," he said, though all children under 14 are at a high risk.
"Teach children to swim, but be advised that such teaching does not absolutely 'drownproof' a child," Auerbach said. "In other words, never let a small child out of your sight when he is near the water, even if he knows how to swim."
Ultimately, Sempsrott said, Eden's story is "remarkable" and one he hopes can be reproduced, "because this was an otherwise very common, hopeless, severe brain damage drowning story." Still, he said, even if this is a one in a million story, for the Carlsons, hyperbaric oxygen treatments have "made all the difference in the world."
"We have no doubt that as she grows, the walking will become easier for her," Carlson wrote of her daughter's progress. "Eden is doing really well today."